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[34.02] Physical Properties of the Deep Impact Target Comet 9P/Tempel 1 from Spitzer and Hubble Space Telescope Observations

C.M. Lisse (UMD/JHU-APL), M.F. A'Hearn (UMD), M.J.S. Belton (Belton Space Initiatives, Inc.), Y.R. Fernandez (UH), O. Groussin (UMD), P. Lamy (Laboratoire d�Astronomie Spatiale), K.J. Meech (UH), I. Toth (Konkoly Observatory), H.A. Weaver (JHU-APL)

Comet 9P/Tempel 1 is the target of the Deep Impact mission to be launched at the end of this year. Accurate knowledge of the physical properties of the comet�s nucleus is important for mission success. Current published size estimates for the nucleus are uncertain by 50% [Fernandez et al. 2003] and the current best rotational solutions have periods of 22 and 42 hours [Belton and Meech, 2004].

In Spring 2004, with the comet outside the ice line and inactive and inbound on the final leg before the DI encounter, we obtained 12 spectrophotometric (7.5-40 microns) visits of the nucleus with the Spitzer Space Telescope over a 40 hour period in March 2004, and 18 photometric (F606) visits over a 42 hour period in May 2004 with the Hubble Space Telescope. Collating these observations into lightcurves, we have applied rotational and thermal models [Belton et al. 2005, Groussin et al. 2004] to derive values for the effective radius, axial ratio, pole position, bulk surface albedo, active surface area, and thermal inertia. Initial analysis of the observations has yielded a nucleus with an average radius of about 3 km, an axial ratio of about 3, a geometric albedo of about 4%, and an active surface fraction of about 8%. The thermal inertia is low, similar to that of other primitive bodies. The rotation pole orientation's J2000 RA and Dec are either (99^o,-19^o) or (60^o,+72^o) , with an error of about 4 degrees. We present the latest results of our observations and analysis here.

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The author(s) of this abstract have provided an email address for comments about the abstract: lisse@astro.umd.edu

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.